Earthquakes Lecture Four

Did you know we have earthquakes in Swain County?

How the Crust is Deformed

Deformation – The bending, tilting, and breaking of the earth’s crust.

Plate Tectonics, the movement of the lithospheric plates, is the major cause of crustal deformation.

Isostasy and Isostatic Adjustment

Isostasy - The state of gravitational equilibrium between the lithosphere and the asthenosphere of the Earth such that lithospheric plates "float" at a given elevation depending on their thickness.

http://youtu.be/G9rN7qhUQZg

Removal of a large load should cause the crust to float up higher, while loading of crustal rocks should make the crust sink deeper.

These forces act like pulling a rubber band gradually until the band snaps. This theory is known as the "elastic rebound theory."

Three Major Earthquake Zones

Ring of Fire

This is a map of the major oceanic spreading centers.

Mid-Ocean Ridges

The mountains along this section were created by three plates colliding together.

The Eurasian - Melanesian Belt -

Stress causes strain in crustal rock. Strain is a change in the shape or volume of rock.

There are three main types of stress

squeezes the rocks of the crust causing the rocks to take up less space and become denser

Compression

  The ends of the rock end up being thicker and the middle is stretched out and becomes thinner. 

Tension pulls rocks causing them to stretch over a larger area.

when rock of the crust pushes in two opposite directions and usually results in a simple bend or break.

Shearing

Earthquakes are vibrations in the earth’s crust

Movement between plate and along faults is not smooth! They move in jerks, giving rise to

earthquakes.

Earthquakes create seismic waves which shake the ground as they pass just like waves of water moving across the ocean.

Types of Seismic Waves

Earthquakes generate three major types of seismic waves

P, for "Primary"

S, for "Secondary" waves

L, for “Long” waves

A drop disturbs the flat surface of the water and creates waves that travel outward in all directions from the disturbance.

Earthquake waves travel the same way

P Waves - Primary

The P waves move in a compressional motion similar to the motion of a slinky

Move the fastest and are the first recorded by a seismographic

Can travel through liquids, gases and solids

S Waves - Secondary

S waves move in a shear motion perpendicular to the direction the wave is traveling.

Secondary Waves are the second to be recorded by a seismograph,

Can only travel through solid materials

P and S waves

L Waves – Long Waves or Surface Waves

Surface or L waves occur only in the earth's crust and cause the most damagetravel along the surface of the earth from the point directly above the quake or epicenterSlowest moving waves, last to be recorded by a seismograph. wave visualization

Shadow Zones are places that do not receive any

earthquake waves

The shadow zone is the area of the earth from angular distances of 104 to 140 degrees from a given earthquake that does not receive any direct P waves. The shadow zone results from S waves being stopped entirely by the liquid core and P waves being bent (refracted) by the liquid core.

Recording Earthquakes

An earthquake is a sudden shaking of the ground. They generate seismic waves which can be recorded on a sensitive instrument called a seismograph.

Earthquake Measurement

Richter Scale expresses the magnitude or measure of energy released by an earthquake.

Advances in seismograph technology have increased our understanding of both earthquakes and the Earth itself.

Focus

Epicenter

wave visualization 2

Finding the Origin of an Earthquake

The FOCUS of an earthquake is where slippage first occurs along the fault line

The EPICENTER is where the earthquake waves reach the earth’s surface directly above the focus

Scientist must have information from three seismographic stations at different locations to plot the epicenter of an earthquake

AftershocksAftershocks are earthquakes that follow the largest shock of an earthquake sequence. They are smaller than the mainshock

Faulting and Folding

Faulting and Folding

Folding is one way to get hills and dips in the landscape. 

What decides if a rock will fault or fold?

Folding If rock bends and does not break, it is called folding. 

Rock becomes very hot when it is compressed.  The hotter it is, the more like it will soften and bend/fold.  The cooler it is, the more brittle it is likely to be (more likely to break/fracture).

Temperature:

The greater the pressure the rock is under, the more likely it is to fold and bend.  One way pressure is produced is by the crustal rocks of our continents pressing down on the rock underneath it.  The extreme weight of all that rock creates a great deal of pressure

Pressure:

Rocks can be made of many different combinations of elements.  Certain elements tend to form rocks that are brittle and other elements tend to form rocks that are more bendable.  How the rock is formed also helps to indicate what it will do under stress.  The rock type could depend on if it cooled quickly during formation, or if it cooled slowly. 

Rock Type:

There are three general types of folds

Synclines

Anticlines

http://www.youtube.com/watch?v=tIFqPNjwB5E

Monoclines

FaultingFaults form in rocks when the stresses overcome the internal strength of the rock resulting in a fracture. A fault can be defined as the displacement of once connected blocks of rock along a fault plane.

Hanging Wall and Footwall

We classify faults by how the two rocky blocks on either side of a fault move relative to each other.

Its name originates from mining activities along large, ancient faults which had since been "filled in" with mineral deposits. Miners could hang their lamps from the wall above them, coining the term "hanging wall" for this side of a fault.

Hanging Wall

FootwallThe counterpart of the hanging wall, the footwall is the part of the Earth's crust below a fault. As with the hanging wall, the" footwall" was so named by miners, since they would walk on the lower side of a mined-out fault.

There are several different kinds of faults

Normal faults occur when tensional forces act in opposite directions and cause one slab of the rock to be displaced up and the other slab down

http//youtu.be/tJDnfT1pqhQ

                                    

Reverse faults develop when compressional forces exist. Compression causes one block to be pushed up and over the other block

http://youtu.be/4b81nXSVA34

Thrust faults:  this is when the hanging wall is actually forced up onto and over the foot wall due to compression in the rock.

http://youtu.be/aHljDIDf6js

You can tell the relative age of rock by igneous intrusions and faulting

Igneous intrusion D is younger than strata layers A, B, and C, but not youngerthan fault line E

Geohazard Risks and Precautions

Landslides EarthquakesTsunamisSinkholesGroundwater pollutionFlooding

Geohazard Safety

Stocking up now on emergency supplies can add to your safety and comfort during and after an earthquake. Store enough supplies for at least 72 hours.

Earthquake visualization

What are the chances we will have an

earthquake in Swain County?

What should we do as precautionary

measures?risk visualization

Stay CalmIf You Are Indoors

Protect yourself from falling debris by standing in a doorway or crouching under a desk or table.

If You Are In An AutomobileStay away from power lines, tunnels, tall buildings,and bridges, and stay in car until the tremors cease.

After an earthquake be cautiousCheck for fire and fire hazards.

Watch for broken glass

Avoid downed power lines

Scientists are trying to make more accurate predictions by detecting changes in the earth’s crust.Faults have been located and mapped

Instruments placed along faults measure small changes in rock movement.

Tsunamis

A wave train, or series of waves, generated in a body of water by an impulsive disturbance that

vertically displaces the water column.

Indonesia Earthquake and Tsunami

Feel: An Earthquake. tsunami.noaa

See: Any unusual water or wave behavior including oddbubbles, whirlpools or water receding or surging inland.

Hear: An unusual noise from out to sea.

If you experience any of these signs, you should evacuate to high ground and tell others that a tsunami may be approaching. It is always better to be safe than sorry.

What do I do during a Tsunami?Use your senses!

Heavy rains can turn terrain unstable and cause land and mudslides.

•Do not build near steep slopes, mountain edges, drainage ways or natural erosion valleys.•Get a ground assessment of your property.

Newfound Gap

Landslides

Landforms created when sediment, or rock is dissolved by groundwater. A sinkhole may formby the ground collapsing on itself to form a hole. Florida has more sinkholes that any other state

Sinkhole

The best thing is prevention and conservation practices to protect important groundwater supplies from being contaminated or depleted in the first place.

Groundwater Pollution

Flooding can carry waste materials from barnyards, sewers, septic tanks, cesspools, and pit privies into a well. Water from a well that may have been flooded should not be used for drinking until the well has been sampled and found to be safe.

Flooding

Tuckaseegee River